The present invention relates antennas and methods for manufacturing the same, and more particularly to a method for manufacturing a slot pattern in an antenna. The present invention is suitable for a plane antenna for use with a frequency band of 50 GHz or higher in a wave guiding space.
The recent highly information-oriented society has universally utilized radio communication systems, and drastically developed them particularly in the microwave and millimeter wave ranges that may transmit large information content. A plane antenna is a suitable input/output (“I/O”) device for short-wavelength radio system among these communication systems, and is expected applicable to many fields including radio LANs and automobile collision prevention radars. The antenna size should correspond to a wavelength of an electric or electromagnetic wave, and should be required smaller as the I/O device for shorter wavelengths. Thereby, the fine process has been required for the recent antenna to maintain its size accuracy.
Conventional antennas include, for example, a dielectric antenna disclosed in Japanese Laid-Open Patent Application No. 56-32807 and a continuous stub antenna disclosed in Japanese Laid-Open Patent Application No. 6-77723.
However, it has become difficult to for conventional manufacturing methods to precisely and cost-efficiently provide plane antennas. The conventional methods rely upon the etching technology to form, for example, a slot pattern and patch pattern in an antenna, and the fine process drastically affects antenna characteristics. However, the etching technology cannot precisely produce the pattern disadvantageously. In particular, the size accuracy in the millimeter wave range requires 1% or higher of the wavelength and, for example, several tens of micrometers for 50 GHz. When a multiplicity of resonant slots and patch patterns are arrayed, stricter size accuracy control is required to maintain directivity. For this demand it is conceivable to apply the fine processing technology that has been usually used for the LSI fabrications, but this technology cannot provide inexpensive antennas.
The conventional plane antenna has formed a slot, for example, using etching. As shown in sectional view of a pattern in FIG. 14A, the conventional plane antenna 300 coats conductor 320 on plate dielectric 310, and forms a slot at a portion (or a concave) uncoated by the conductor 320. Here, FIG. 14A is a schematic, partially sectional view near a surface of the conventional plane antenna. As shown, the conductor 320 defines the slot 330. However, the conductor 320 erodes, as shown in FIG. 14B, when water 340 is collected in the concave 330 and, as indicated by broken lines, deteriorates and turns into the conductor 320A as shown in FIG. 14C. As it is understood from a comparison between an arrow between the broken lines and an arrow between the solid lines, an interval of the slot 330 changes and the plane antenna 300 varies its property. Here, FIG. 14B is a schematic sectional view showing that the water 340 is collected in the slot 330 shown in FIG. 14A, and FIG. 14C is a schematic sectional view of changing widths of the slot 330 in the plane antenna 300 as a result of FIG. 14B.
The antenna disclosed in Japanese Patent Application No. 56-32807 has, as shown in FIG. 6(d), a flat conductor around a slot, thereby easily collecting water and resulting in erosion of the slot. As a result, the slot width varies as discussed above. The antenna disclosed in Japanese Laid-Open Patent Application No. 6-77723 is a continuous cross stub device that has a long slot extending in one direction without the resonant slot. The stub device may maintain the antenna property even when the slot partially erodes in its longitudinal direction and the slot interval changes in one part, because the slot interval in other parts does not change. Therefore, this stub device is relatively corrosion resistant. However, another and separate countermeasures should be taken for such an antenna that is required to be corrosion resistant in a slot's longitudinal direction, such as a plane antenna having a resonant slot.